factor an expression into two expressions

I have a function a=3/(1+e*cos(f)) where both e and f are symbolic variables. I would like to write this function as the sum of two expressions B and G where a=B+e*G. For this example problem, I know that B=3 and G=(-3*cos(f))/(1+e*cos(f)). What commands in Matlab would allow me to write this expression in this form? Thank you.